Incorporation of chemical functionalities in the framework of mesoporous silica

Mesoporous silica, which shows well-defined pore systems, tunable pore diameters (2-30 nm), narrow pore size distributions and high surface areas (>600 m(2) g(-1)), is frequently modified using different methodologies (including in situ and post-synthetic strategies) to introduce various chemical functionalities useful in applications like catalysis, separation, drug delivery, and sensing. This contribution aims to provide a critical overview of the various strategies to incorporate chemical functionalities in mesoporous silica highlighting the advantages of the in situ methods based on the bottom-up construction of mesoporous silica containing various chemical functionalities in its structure.     

A nonlocal diffusion problem on manifolds

ABSTRACT

In this paper we study a nonlocal diffusion problem on a manifold. These kinds of equations can model diffusions when there are long range effects and have been widely studied in Euclidean space. We first prove existence and uniqueness of solutions and a comparison principle. Then, for a convenient rescaling we prove that the operator under consideration converges to a multiple of the usual Heat-Beltrami operator on the manifold. Next, we look at the long time behavior on compact manifolds by studying the spectral properties of the operator. Finally, for the model case of hyperbolic space we study the long time asymptotics and find a different and interesting behavior.     

13C solid-state NMR complemented by ATR-FTIR and micro-DSC to study modern collagen-based material and historical leather

Ancient vegetable tanned leathers and parchments are very complex materials in which both different manufacturing and deterioration processes make their study and chemical characterisation difficult. In this research, solid-state nuclear magnetic resonance (NMR) spectroscopy was applied to identify different tannin families (condensed and hydrolysable) in historical leather objects such as bookbindings, wall upholsters, footwear and accessories, and military apparel. Furthermore, leather deterioration with special focus on collagen gelatinisation was investigated. A comparison with Fourier transform infrared (FTIR) spectroscopy and micro-differential scanning calorimetry (micro-DSC) was also performed to support the ¹³C CP-MAS NMR findings and to point out the advantages and limitations of solid-state NMR in analysing historical and archaeological leathers. A wide database of NMR and FTIR spectra of commercial tannins compounds was also collected in order to characterise historical and archaeological leathers.     

Enhancement of continuously rotating detonation in hydrogen and oxygen-enriched air

The enhancement of continuously rotating detonation in oxygen-enriched air was demonstrated in an annular rotating detonation combustor (RDC) under a diffusive supply of hydrogen and an oxidizer. Experimental tests were performed to reveal the effects of oxygen volume fraction, mass flow rate, and equivalent ratio on the propagation of continuously rotating detonation wave (CRDW). It is observed that an increase in the air mass flow rate from 25 g/s to 225 g/s causes an increase in the propagation velocity of the stable CRDW in the RDC. For an oxygen volume fraction up to 35%, the difference between the propagation velocity of detonation and the theoretical Chapman–Jouguet value is less than 5%. Under the chemical stoichiometric ratio condition for air, the CRDW is stabilized when the air mass flow rate reaches 185 g/s. However, stabilized CRDW is observed even when the air flow rate is only 45 g/s under the presence of 30% or 35% oxygen. Increase in the oxygen volume fraction leads to an extension of the rich/lean limit for generating a stable CRDW. This study aims to provide guidance for the modulation of continuously rotating detonation.     

Distinguishing Activities in the Photodynamic Arsenals of the Pigmented Ciliates Blepharisma sinuosum Sawaya, 1940 and Blepharisma japonicum Suzuki, 1954 (Ciliophora: Heterotrichea)

Blepharismins are photodynamic hypericin-like dianthrones produced as a variable pigment blend in Blepharisma ciliates and mostly studied in the Afro-Asiatic Blepharisma japonicum. The present work describes the bioactivity of pigments from the Brazilian Blepharisma sinuosum. Comparative analyses showed that the pigments from both species can trigger photo-induced modifications in phospholipids, but different redox properties and biological activities were assigned for each pigment blend. Stronger activities were detected for B. sinuosum pigments, with the lethal concentration LC₅₀ 10 × lower than B. japonicum pigments in light-irradiated tests against Bacillus cereus and less than half for treatments on the human HeLa tumor cells. HPLC showed B. sinuosum producing a simpler pigment blend, mostly with the blepharismin-C (~ 70%) and blepharismin-E (~ 30%) types. Each blepharismin engaged a specific dose–response profile on sensitive cells. The blepharismin-B and blepharismin-C were the most toxic pigments, showing LC₅₀ ~ 2.5–3.0 µm and ~ 100 µm on B. cereus and HeLa cells, respectively, after illumination. Similarity clustering analysis compiling the bioactivity data revealed two groups of blepharismins: the most active, B and C, and the less active, A, D and E. The B. sinuosum pigment blend includes one representative of each clade. Functional and medical implications are discussed.     

A rheological modelling and microscopic analysis of bigels

Bigels are two-phase systems in which each phase (organic or aqueous) is structured using a specific gelator. Currently, these systems are widely investigated, mainly as matrices for controlled drug delivery, because they possess the advantages of both organogels and hydrogels and are very stable owing to the structuration of the dispersing phase. A deeper knowledge of the relationship between macroscopic properties and microscopic parameters seems necessary to aim at designing materials with specific rheological properties and suitable for specific uses. From a rheological point of view, bigels can be considered as composite materials in which a structured system (organogel or hydrogel, according to the desired use) is dispersed in a gelled continuous phase. In the present paper, a number of rheological models, already proposed in literature for composite systems, were used to relate the bigel complex modulus to the rheological properties of dispersed and continuous phase and to their volumetric ratio. It was observed that these models are not able to describe properly bigel behaviour, probably owing to some theoretical assumptions such as the uniform distribution of spherical particles. An empirical modification of a literature model, proposed to take into account some peculiarities of bigels, yields an improvement of fitting even if further investigations are necessary to better understand the effects of particle size distribution and morphology on observed properties.     

Kinetic Enhancement of Direct Hydrogenation of MgB2 to Mg(BH4)2 upon Mechanical Milling with THF,MgH2, and/or Mg

Modification of magnesium diboride, MgB₂, by mechanical milling with THF, MgH₂, and/or Mg results in a lowering of the conditions required for its direct, bulk hydrogenation to magnesium borohydride, Mg(BH₄)₂, by 300 bar and 100 °C. Following mechanical milling with MgH₂ or THF and Mg, MgB₂ can be hydrogenated to Mg(BH₄)₂ at 300 °C under 700 bar of H₂ while achieving ∼54–71 % conversion to the borohydride. The discovery of a means of dramatically lowering the conditions required for the hydrogenation of MgB₂ is an important step towards the development of a practical onboard hydrogen storage system based on hydrogen cycling between Mg(BH₄)₂ and MgB₂. We suggest that mechano-milling with THF, Mg, and/or MgH₂ may possibly introduce defects in the MgB₂ structure which enhance hydrogenation. The ability to activate the MgB₂ through the introduction of structural defects transcends its relevance to hydrogen storage, as a method of overcoming its chemical inertness provides the key to harnessing other interesting properties of this material.     

Uniqueness of solution to a free boundary problem from combustion

We investigate the uniqueness and agreement between different kinds of solutions for a free boundary problem in heat propagation that in classical terms is formulated as follows: to find a continuous function defined in a domain and such that

0\}. \end{displaymath}">

We also assume that the interior boundary of the positivity set, \nobreak 0\}$">, so-called free boundary, is a regular hypersurface on which the following conditions are satisfied:

Here denotes outward unit spatial normal to the free boundary. In addition, initial data are specified, as well as either Dirichlet or Neumann data on the parabolic boundary of . This problem arises in combustion theory as a limit situation in the propagation of premixed flames (high activation energy limit).

The problem admits classical solutions only for good data and for small times. Several generalized concepts of solution have been proposed, among them the concepts of limit solution and viscosity solution. We investigate conditions under which the three concepts agree and produce a unique solution.

     

S-(2-pyridinyl)-1,1,3,3-tetramethylthiouronium hexafluorophosphate. A new reagent for the synthesis of 2-pyridinethiol esters

[reaction: see text] A new thiouronium-based reagent for the synthesis of 2-pyridinethiol esters under non-nucleophilic conditions from the corresponding carboxylic acids was developed. The resulting procedure enables the preparation of previously unavailable alpha,beta-unsaturated 2-pyridinethiol esters as well as their aliphatic and aromatic counterparts.